Drug resistance invariably develops over the course of continuing chemotherapy. Overcoming this problem is a major challenge in the treatment of cancer. Indeed, tumor cells utilize multiple mechanisms to increase their resistance to chemotherapeutic drugs. For example, tumor cells may overexpress the multiple drug resistant transporter and oncoprotein epidermal growth factor receptor genes, as well as induce the activity of NF-E2-related factor 2, a redox-sensing transcription factor that upregulates a wide spectrum of genes involved in glutathione metabolism and drug detoxification. See (Huang et al., 2005a; Makarovskiy et al., 2002; Wang et al., 2010); (Salzberg et al., 2007; Sirotnak et al., 2000); (Singh et al., 2010; Zhang et al., 2010); and (Huang and Sadee, 2003; Seruga et al., 2010). The Hedgehog pathway is another cell signaling pathway that is involved in chemoresitance. (Domingo-Domenech et al., 2012).
To date, no single agent that was designed to target a specific mechanism of resistance has been found to be effective. However, the small molecule, wilforlide A, which can be extracted from the Chinese medicinal herb, Triperygium wilfordii, sensitizes cancer cells that have become resistant to chemotherapeutic drug therapy, so that the cancer once again becomes sensitive to the chemotherapeutic drug.